Understanding ISO Underwater

Understanding ISO Underwater

Understanding ISO Underwater

What ISO stands isn’t going to give you much of a clue as to what it does. ISO simply stands for International Standardisation Organisation, nothing much to pick from that. Back in the 70’s two film standards (ASA & DIN) combined to make a standard measure for film sensitivity. Modern digital manufacturers have kept to the same measurements to maintain similar brightness levels as film. Essentially ISO tells your camera how bright the photo should be. Very simply put it brightens or darkens your image. It doesn’t physically affect the amount of light that’s hitting your sensor like aperture and shutter speed.

One Of The Three Pillars Of Photography

Along with aperture and shutter speed, ISO is one of the essential three pillars of photography. Important settings that you need to understand if you want to get out of auto mode and make the most of your photo opportunities. Eventually we’ll cover all of them but we’ll start with ISO.

Cameras will have varying ISO values, a common one for compact cameras would ISO 100 – 6400. The levels usually double with each step. For example from low to high: ISO 100, 200, 400, 800, 1600, 3200, 6400

Every time you step up, you’re basically doubling the brightness of your image. However this does come with a caveat, the higher the ISO the more noise you’ll get on your photo. With high end DSLR’s you’ll have much more room to play with but not with compact cameras. For the best image quality keep the ISO as low as possible. Try adjusting shutter speed and aperture before raising the ISO.

The brightness will have to be ignored, my camera doesn’t allow manual shutter speed. However you can clearly see the noise level and dynamic range difference from ISO settings of 100 & 6400

understanding iso comparison

understanding iso comparison

If you’re using strobes, internal flash or a video light, the lowest ISO setting in your camera should be fine. You should get the highest dynamic range and more colour sensitivity. Obviously underwater we don’t have much light to work with so if you haven’t got a light source keeping a low ISO is going to result in dark photos.

What Is Digital Noise?

There are two basic types of noise in digital photography:

Digital Noise – Can be caused by electricity or heat within the camera itself.

Photon Noise – Photons of light randomly reflecting and picked up by the camera sensor.

Both are always there but if you have the camera settings correct, they’ll be hidden by the light of the image you’re trying to capture. Increasing the ISO on your camera makes the sensor more sensitive and so more likely to capture the noise.

What Can I Do?

Above water, lowering shutter speed and reducing f- stop will increase the light that hits the cameras sensor. So you can try that but you’ll have to be perfectly still and the subject not moving. A perfect storm that is extremely difficult to achieve underwater. Try raising your ISO step by step until you find the highest on your particular camera that doesn’t significantly raise the noise.

Most modern cameras will have a noise reduction setting hidden away somewhere in the menu. Dust off your manual and make sure that you have it turned on.

All this is covered in the very good PADI Underwater Photo specialty, all aspects of underwater photography are covered and you’ll receive a great manual with lots of useful hints and tips. To find our more go to our page here

So It’s Just Like Brightening A Photo In Photoshop

Not quite, although the effect is basically the same. The image will brighten and you will get more grain. Generally you’ll get a better result raising your ISO on the camera than you will brightening with computer software. Some of the popular editing apps for underwater photos simply do this, you’ll notice the image brighten but quality will be reduced. You could raise the ISO on your camera and get the same effect with slightly better quality.

So next time you’re set for an underwater adventure, make sure you get the ISO setting correct for your camera.

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By Justin Hartrey

I've been enjoying the incredible marine life in our oceans for over 25 years. 13 years ago I became a PADI professional, hoping to introduce as many people as possible to the incredible beauty of the seas.

Having been fortunate enough to dive all over south east and especially Thailand, I enjoy sharing my experience and passion on this blog.

Posted in Photo Tips & Tricks on .

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